If we choose to live near convergent plate boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. Yes, convergent boundaries are dangerous places to live, but with preparation and watchfulness, the danger can be lessened somewhat.
Nitrification, as stated above, is formally a two-step process; in the first step ammonia is oxidized to nitrite, and in the second step nitrite is oxidized to nitrate. Different microbes are responsible for each step in the marine environment.
It is composed of four basic steps: nitrogen fixation, nitrification, ammonification, and denitrification. During nitrogen fixation, nitrogen gas from the air is converted into ammonium. During nitrification, ammonium is converted into nitrates, which are taken up by plants. The nitrates are used by the plants and animals, then returned to ammonium using ammonification.